1. Field
The present specification generally relates to systems for differential optical signaling and, more specifically, to systems for differential optical signaling of M-ary modulation formats.
2. Technical Background
Short reach high-speed optical interconnects can be utilized for a variety of high performance computer and datacenter applications. In many optical interconnects such as laser/external modulator links operating with on-off keying, about one half of the optical power generated by a laser is unused. Specifically, the external modulator links generally suppress the laser power during the off state. Moreover, when on-off keying modulation is received, the optimum decision threshold can float relative to the received optical power, i.e., the higher the power, the higher the threshold. Accordingly, the optimum decision threshold adapts with the optical signal power or the noise variances in the one and zero states.
Optical differential signaling generally includes the transmission of two or more complementary signals on multiple separate transmission channels. The complementary signals can be combined upon receipt to extract data encoded in the signals. Optical differential signaling can be difficult to implement in an optical fiber transmission system due to the cost of matched group delay and regeneration. Wavelength division multiplexing in a single fiber can be used to overcome the difficulties associated with matching optical fiber delays when using two discrete fibers. However, it can be difficult to generate such a modulated signal with a single modulator. Moreover, the chromatic dispersion of the link must be matched in wavelength division multiplexing.
Accordingly, a need exists for alternative systems for differential optical signaling.